Traction drive fluid compositions

ABSTRACT

A traction drive fluid composition which comprises component (A) a base oil for traction drives bearing at least one selected from a quaternary carbon atom or an alicyclic structure in the molecule and component (B) at least one polymer having a weight average molecular weight in the range of 8,000 to 40,000 and which is selected from among (a) hydrocarbon polymers each containing as a constituent at least 10 mole % of a monomer bearing a cyclic structure, (b) hydrocarbon polymers each containing at least 25% of quaternary carbon atoms in the backbone chain, and (c) hydrogenated products from the polymers (a) and (b). The traction drive fluid composition is improved in viscosity index without lowering the traction coefficient to a level lower than that of the base oil and is excellent in shear stability.

TECHNICAL FIELD

The present invention relates to a traction drive fluid composition,more particularly to a traction drive fluid composition which isimproved in viscosity index and is excellent in shear stability, and inwhich its traction coefficient is not lower than that of a base oil.

BACKGROUND ARTS

Since a traction drive type continuously variable transmission (CVT)used for an automobile has a large torque transmission capacity and isused under severe conditions, it is indispensable from the viewpoint ofpower transmission that a traction oil to be used in a CVT has atraction coefficient which is sufficiently higher than a lowest value inthe range of working temperature, that is, the traction coefficient at ahigh temperature (140° C.) is sufficiently higher than a design value ofa CVT.

The traction oil, which also plays a role as an ordinary lubricating oilin a CVT, is required to have high viscosity capable of maintainingsufficient oil films even at a high temperature to prevent frictionand/or wear and at the same time, to have low viscosity even at a lowtemperature for the sake of low temperature startup in cold districtssuch as North America and North Europe. That is to say, it is necessarythat the traction oil has a high viscosity index minimized in variationin viscosity with temperature.

On the basis of the understanding of the above-mentioned background, thepresent inventors developed a high performance base oil which is for atraction oil and which has a high traction coefficient at a hightemperature and a high viscosity index, said high performance has neverheretofore been realized {Japanese Patent Application Laid-Open No.17280/2000 (Heisei 12)}, but from the aspect of practical application,there was need to further add a viscosity index improver to the base oilthus developed. However, since even a small amount of addition of apreviously known viscosity index improvers markedly lowers tractioncoefficient at a high temperature, it has been eagerly desired todevelop a viscosity index improver which can improve viscosity indexwithout lowering the traction coefficient of a base oil and which iswell suited for traction oils.

There is disclosed in Japanese Patent Application Laid-Open No.19698/1986 (Showa 61), a traction oil composition which comprises a baseoil and a hydrogenation product of a thermoplastic resin bearing anaromatic ring blended therewith, and which is enhanced in viscosityindex and traction coefficient. However, it is impossible to judgewhether the composition is excellent or not from the practicalapplication, since it is highly volatile owing to a low molecular weightand is composed of practically unsuitable bicyclohexyl compound as abase oil.

There is disclosed polymethacrylate having an alicyclic structure as aviscosity index improver for traction oils {for instance, refer toJapanese Patent Application Laid-Open No. 19697/1986 (Showa 61),Japanese Examined Patent Application Publication No. 62984/1994 (Heisei6) and Japanese Patent Application Laid-Open No. 19371/2002 (Heisei14)}. Nevertheless it is difficult to use the same as the case may be,in traction oils under severe working conditions because of insufficientshear stability.

DISCLOSURE OF THE INVENTION

The present invention has been achieved from the above-mentionedviewpoint, and it is an object thereof to provide a traction drive fluidcomposition which is improved in viscosity index, is excellent in shearstability, and is imparted with a traction coefficient not lower thanthat of a base oil.

As the result of intensive extensive research and investigationaccumulated by the present inventors, it has been discovered thatspecific polymers each having a weight average molecular weight in therange of 8,000 to 40,000 possess excellent performances as a viscosityindex improver for traction oils. The present invention has beenaccomplished by the foregoing findings and information.

That is to say, the gist of the present invention is as follows.

-   1. A traction drive fluid composition which comprises component (A)    a base oil for traction drives bearing a quaternary carbon atom    and/or an alicyclic structure in the molecule and component (B) at    least one polymer having a weight average molecular weight in the    range of 8,000 to 40,000 and which is selected from among (a)    hydrocarbon polymers each containing as a constituent at least 10    mole % of a monomer bearing a cyclic structure, (b) hydrocarbon    polymers each containing at least 25% of quaternary carbon atoms in    the backbone chain, and (c) hydrogenated products from the    polymers (a) and (b);-   2. The traction drive fluid composition as set forth in the    preceding item 1, wherein the polymer as the component (B) has a    weight average molecular weight in the range of 9,000 to 38,000;-   3. The traction drive fluid composition as set forth in the    preceding item 1 or 2, wherein the base oil as the component (A) has    a traction coefficient at 140° C. of at least 0.070, kinematic    viscosity at 40° C. in the range of 10 to 25 mm²/s, a viscosity    index of at least 60, a pour point of minus 40° C. or lower and a    flash point of 100° C. or higher;-   4. The traction drive fluid composition as set forth in the    preceding item 1, wherein the polymer as the component (B) is    blended in an amount of 0.1 to 20% by mass based on the composition    with the base oil as the component (A); and-   5. The traction drive fluid composition as set forth in the    preceding item 1, wherein the polymer as the component (B) is    blended in an amount of 0.5 to 5% by mass based on the composition    with the base oil as the component (A).

THE MOST PREFERRED EMBODIMENTS TO CARRY OUT THE INVENTION

In the following, the present invention will be described in detail. Thebase oil bearing a quaternary carbon atom and/or an alicyclic structurein the molecule as the component (A), which is exemplified byisoparaffin bearing a quaternary carbon atom such as polybutene,polyisobutylene, diisobutylene oligomer and the like; naphtheniccompounds bearing an alicyclic structure such as cyclohexane ring,bicycloheptane ring, bicyclooctane ring and the like, needs to have ahigh traction coefficient, and may be above-mentioned base oil that isusually employed as a traction drive base oil. Preferably, the base oilsatisfies the requirements including a traction coefficient at 140° C.being at least 0.070, kinematic viscosity at 40° C. being in the rangeof 10 to 25 mm²/s, a viscosity index of at least 60, a pour point ofminus 40° C. or lower and a flash point of 100° C. or higher.

Of these, are preferable naphthenic compounds bearing at least two ringsselected from among cyclohexane ring, bicyclo [2, 2, 1]heptane ring,bicyclo [3, 2, 1] octane ring, bicyclo [2 2, 2] octane ring and bicyclo[3, 3, 0] octane ring.

Specifically, the base oil can preferably be selected from hydrogenatedproducts from the dimers of at least one alicyclic compound selectedfrom among bicyclo [2, 2, 1]heptane ring-bearing compounds, bicyclo [3,2, 1] octane ring-bearing compounds, bicyclo [2 2, 2] octanering-bearing compounds, and bicyclo [3, 3, 0] octane ring-bearingcompounds; and from cyclohexane ring-bearing compounds such as2,4-dicyclohexyl-2-methylpentane, 2,4-dicyclohexylpentane,2,4-dicyclohexyl-2-methylbutane and1-decahydronaphthyl-1-cyclohexylethane.

A preferable process for the production of the above-stated hydrogenatedproducts from the dimer of alicyclic compound comprises dimerization,hydrogenation and distillation in this order of the under-mentionedolefin in which an alkyl group may substitute.

Examples of the olefin in which an alkyl group such as methyl group,ethyl group or propyl group may substitute include for instance, bicyclo[2, 2, 1]hepto-2-ene; alkenyl-substituted bicyclo [2, 2, 1]hepto-2-enesuch as vinyl-substituted or isopropenyl-substituted bicyclo [2, 2,1]hepto-2-ene; alkylidene-substituted bicyclo [2, 2, 1]hepto-2-ene suchas methylene-substituted, ethylidene-substituted orisopropylidene-substituted bicyclo [2, 2, 1]hepto-2-ene;alkenyl-substituted bicyclo [2, 2, 1]heptane such as vinyl-substitutedor isopropenyl-substituted bicyclo [2, 2, 1]heptane;alkylidene-substituted bicyclo [2, 2, 1]heptane such asmethylene-substituted, ethylidene-substituted orisopropylidene-substituted bicyclo [2, 2, 1]heptane; bicyclo [3, 2, 1]octene; alkenyl-substituted bicyclo [3, 2, 1] octene such asvinyl-substituted or isopropenyl-substituted bicyclo [3, 2, 1] octene;alkylidene-substituted bicyclo [3, 2, 1] octene such asmethylene-substituted, ethylidene-substituted orisopropylidene-substituted bicyclo [3, 2, 1] octene; alkenyl-substitutedbicyclo [3, 2, 1] octane such as vinyl-substituted orisopropenyl-substituted bicyclo [3, 2, 1] octane; alkylidene-substitutedbicyclo [3, 2, 1] octane such as methylene-substituted,ethylidene-substituted or isopropylidene-substituted bicyclo [3, 2, 1]octane; bicyclo [3, 3, 0] octene; alkenyl-substituted bicyclo [3, 3, 0]octene such as vinyl-substituted or isopropenyl-substituted bicyclo [3,3, 0] octene; alkylidene-substituted bicyclo [3, 3, 0] octene such asmethylene-substituted, ethylidene-substituted orisopropylidene-substituted bicyclo [3, 3, 0] octene; alkenyl-substitutedbicyclo [3, 3, 0] octane such as vinyl-substituted orisopropenyl-substituted bicyclo [3, 3, 0] octane; alkylidene-substitutedbicyclo [3, 3, 0] octane such as methylene-substituted,ethylidene-substituted or isopropylidene-substituted bicyclo [3, 3, 0]octane; bicyclo [2, 2, 2] octene; alkenyl-substituted bicyclo [2, 2, 2]octene such as vinyl-substituted or isopropenyl-substituted bicyclo [2,2, 2] octene; alkylidene-substituted bicyclo [2, 2, 2] octene such asmethylene-substituted, ethylidene-substituted orisopropylidene-substituted bicyclo [2, 2, 2] octene; alkenyl-substitutedbicyclo [2, 2, 2] octane such as vinyl-substituted orisopropenyl-substituted bicyclo [2, 2, 2] octane; alkylidene-substitutedbicyclo [2, 2, 2] octane such as methylene-substituted,ethylidene-substituted or isopropylidene-substituted bicyclo [2, 2, 2]octane.

Of these, hydrogenated products from the dimer of bicyclo [2, 2,1]heptane ring-bearing compounds are particularly preferable. Thecorresponding olefin as a starting raw material is specificallyexemplified by bicyclo [2, 2, 1]hepto-2-ene; 2-methylenebicyclo [2, 2,1]heptane; 2-methylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-3-methybicyclo [2, 2, 1]heptane; 3-methylene-2-methybicyclo[2, 2, 1]heptane; 2-3-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-7-methybicyclo [2, 2, 1]heptane; 3-methylene-7-methybicyclo[2, 2, 1]heptane; 2-7-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-5-methybicyclo [2, 2, 1]heptane; 3-methylene-5-methybicyclo[2, 2, 1]heptane; 2-5-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-6-methybicyclo [2, 2, 1]heptane; 3-methylene-6-methybicyclo[2, 2, 1]heptane; 2-6-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-1-methybicyclo [2, 2, 1]heptane; 3-methylene-1-methybicyclo[2, 2, 1]heptane; 1,2-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-4-methybicyclo [2, 2, 1]heptane; 3-methylene-4-methybicyclo[2, 2, 1]heptane; 2,4-dimethylbicyclo [2, 2, 1]hepto-2-ene;2-methylene-3,7-dimethybicyclo [2, 2, 1]heptane;3-methylene-2,7-dimethybicyclo [2, 2, 1]heptane; 2, 3,7-trimethylbicyclo [2, 2, 1]hepto-2-ene; 2-methylene-3,6-dimethybicyclo[2, 2, 1]heptane; 3-methylene-2,6-dimethybicyclo [2, 2, 1]heptane;2-methylene-3,3-dimethybicyclo [2, 2, 1]heptane;3-methylene-2,2-dimethybicyclo [2, 2, 1]heptane; 2, 3,6-trimethylbicyclo [2, 2, 1]hepto-2-ene; 2-methylene-3-ethylbicyclo [2,2, 1]heptane; 3-methylene-2-ethylbicyclo [2, 2, 1]heptane;2-methyl-3-ethylbicyclo [2, 2, 1]hepto-2-ene; and the like.

The above-mentioned dimerization means not only the dimerization of sameolefins but also codimerization of a plurality of different olefins.

The dimerization of an olefin is carried out usually in the presence ofa catalyst by adding a solvent when necessary.

An acidic catalyst is usually employed for the dimerization, and isspecifically exemplified by solid acids such as activated clay, zeolite,montmorilonite and ion exchange resin; hydrofluoric acid; mineral acidssuch as polyphosphoric acid; organic acids such as trifurric acid; Lewisacids such as aluminum chloride, ferric chloride, stannic chloride,boron trifluoride, boron trifluoride complex, boron tribromide, aluminumbromide, gallium chloride and gallium bromide; and organoaluminumcompounds such as triethylaluminum, diethylaluminum chloride andethylaluminum dichloride.

The amount of the above-cited catalyst to be used is not specificallylimited, but is usually in the range of 0.1 to 100% by mass based on thefeed olefin.

In the case of dimerization, a solvent is not always necessary, but isusable in view of the handling of the feed olefin and the catalyst atthe time of reaction or the control of proceeding of reaction. Examplesof such solvents include saturated hydrocarbon such as various pentane,various hexane, various octane, various nonane and various decane;alicyclic hydrocarbons such as cyclopentane, cyclohexane,methylcyclohexane and decalin; ether compounds such as diethyl ether andtetrahydrofuran; halogen-containing compounds such as methylene chlorideand dichloroethane and nitro compounds such as nitrometahne andnitrobenzene.

In the case of dimerization in the presence of the catalyst, thereaction temperature is generally in the range of minus 70 to 200° C.Proper reaction conditions are set in the temperature range depending onthe types of catalyst and additives, including a reaction pressure beingusually atmospheric pressure and a reaction time being usually in therange of 0.5 to 10 huors.

Subsequently, the dimer of feedstock olefin thus obtained ishydrogenated to produce the objective hydrogenated product of dimer,wherein the hydrogenation may be carried out by properly mixingdifferent dimers which have been dimerized by using individual feedstockolefin separately.

The hydrogenation reaction is carried out usually in the presence of acatalyst, which is exemplified by hydrogenation catalyst such as nickel,ruthenium, palladium, platinum, rhodium and iridium.

The amount of the above-cited catalyst to be used is usually in therange of 0.1 to 100% by mass based on the dimerized products.

While the hydrogenation reaction proceeds in the absence of a solvent asis the case with the above-stated dimerization reaction, a solvent canbe used, and is exemplified by saturated hydrocarbon such as variouspentane, various hexane, various octane, various nonane and variousdecane; alicyclic hydrocarbons such as cyclopentane, cyclohexane,methylcyclohexane and decalin It is possible to proceed with thehydrogenation reaction at a reaction temperature of usually of 20 to300° C., a reaction pressure of atmospheric pressure to 20 Mpa and areaction time of usually 1 to 10 hours. The resultant hydrogenatedproduct may be mixed with other hydrogenated product which has beenformed from separate feedstock olefin in a separate step so that theresultant mixture is used as the base oil as the component (A).

Next, the viscosity index improver as the component (B) to be mixed withthe base oil as the component (A) is at least one polymer which has aweight average molecular weight in the range of 8,000 to 40,000 andwhich is selected from among (a) hydrocarbon polymers each containing asa constituent at least 10 mole % of a monomer bearing a cyclicstructure, (b) hydrocarbon polymers each containing at least 25% ofquaternary carbon atoms in the backbone chain, and (c) hydrogenatedproducts from the polymers (a) and (b).

The weight average molecular weight of the polymer as the component (B),when being less than 8,000, leads to extremely small working effect onviscosity index improvement, whereas said molecular weight, when beingmore than 40,000, brings about inferior shear stability causing severedpolymer chain on use and marked decrease in permanent viscosity, thusrendering the polymer unsuitable and unfavorable as a viscosity indeximprover for traction oils. The weight average molecular weight thereofis in the range of preferably 9,000 to 38,000, more preferably 9,000 to35,000, particularly preferably 10,000 to 35, 000.

The monomer bearing a cyclic structure in item (a) is exemplified byaromatic monomers such as styrene, p-methylstyrene, α-methylstyrene,vinylnaphthalene and indene; alicyclic monomers such asvinylcyclohexane, vinylcyclohexene, cyclohexene, dipentene and limonene;and crosslinked cyclic monomers such as bicycle [2, 2, 1]heptene;methylbicycle [2, 2, 1]heptene; dimethylbicycle [2, 2, 1]heptene;dicyclopentadiene; dihydrodicyclopentadiene; and tetracyclo [6. 2. 1.1^(3.6) 0 ^(2.7)] dodecene.

The hydrocarbon polymer as the component (a), which is a polymer of theforegoing monomer bearing a cyclic structure, or a copolymer of saidmonomer bearing a cyclic structure and an aliphatic monomer such asethylene, propylene, butene, butadiene, pentene, hexene, heptene,octene, nonene and decene, contains at least 10 mole % of a monomerbearing a cyclic structure. The monomer content of less than 10 mole %is unfavorable because of lowered traction coefficient, the content ofat least 20 mole % is preferable, and at least 40 mole % is morepreferable.

The hydrocarbon polymers as the component (b) are those each containingat least 25% of quaternary carbon atoms in the backbone chain, areexemplified by polyisobutylene, isobutylene/ethylene copolymer,isobutylene/propylene copolymer, isobutylene/butene copolymer and thelike, and contain at least 50 mole % of isobutylene in the case ofisobutylene copolymer. The content of quaternary carbon atoms in thebackbone chain of less than 25% is unfavorable because of loweredtraction coefficient, the content of at least 30 mole % is preferable,and at least 40 mole % is more preferable.

The hydrocarbon polymers as the component (c) are each a hydrogenatedproduct from the polymers (a) and (b). Since an olefinic double bonddeteriorates antioxidation stability when remaining in the polymer, itis desirable to completely remove all of olefins. In the case of polymerbearing aromatic rings, the aromatic rings may be hydrogenated in wholeor in part. The degree of hydrogenation of the aromatic rings may beregulated at need in accordance with the solubility in the base oil.

The blending ratio of the component (B) (viscosity index improver) tothe component (A) (base oil), which cannot be unequivocally determinedbut is determined by the viscosity of the base oil, is in the range ofpreferably 0.1 to 20% by mass. The blending ratio thereof, when beingless than 0.1% by mass, sometimes results in failure to exert the effecton viscosity index improvement, whereas the blending ratio, when beingmore than 20% by mass, sometimes brings about excessively highlow-temperature viscosity and besides, marked decrease in permanentviscosity. In view of the foregoing, the blending ratio is in the rangeof preferably 0.5 to 5% by mass.

It is possible to use the traction drive fluid composition according tothe present invention by blending therewith at need, a proper amount ofany of additives including viscosity index improvers other than theforegoing, antioxidants, rust preventives, detergent dispersants, pourpoint depressants, extreme pressure additives, antiwear agents, oilnessimprovers, antifoaming agents, corrosion inhibitors and the like.

EXAMPLE

In what follows, the present invention will be described morespecifically with reference to working examples, which however shallnever limit the present invention thereto.

Reference Example 1

An autoclave made of stainless steel and having a capacity of two literwas charged with 561 g (8 mole) of crotonaldehyde and 352 g (2.67 mole)of cyclopentadiene, so that the contents therein was reacted at 170° C.for 3 hours under stirring. The resultant reaction solution was cooledto room temperature, and thereafter 18 g of Raney nickel catalyst(available from Kawaken Fine Chemicals Co., Ltd. under the trade nameM-300T) to proceed with hydrogenation reaction under a hydrogen pressureof 0.9 MPa·G at a reaction temperature of 150° C. for 4 hours. Aftercooling the resultant reaction solution, the catalyst was filtered off,and the filtrate was subjected to vacuum distillation to produce 565 gof a fraction at 105° C./2.66 kPa. As a result of analysis of theresultant fraction by means of mass spectrum and nuclear magneticresonance spectrum, the fraction was confirmed to be2-hydroxymethyl-3-methylbicyclo [2. 2. 1]heptane.

Subsequently, in a flow system atmospheric tubular reactor made ofquartz glass measuring 20 mm in outer diameter and 500 mm in length wasplaced 20 g of gamma alumina (available from Nikki Chemical IndustrialCo., Ltd. under the trade name N612) to carry out dehydration reactionat a reaction temperature of 285° C. at a weight hourly space velocity(WHSV) of 1.1 hr⁻¹. As a result, there was obtained 490 g of adehydration reaction olefinic product of

-   2-hydroxymethyl-3-methylbicyclo [2.2.1]heptane containing-   2-methylene-3-methylbicyclo [2. 2. 1]heptane and-   2-hydroxymethyl-3-methylbicyclo [2. 2. 1]hepto-2-ene.

In a four-neck flask having a capacity of one liter were placed 10 g ofboron trifluoride diethyl ether complex and 490 g of the previouslyobtained olefinic compound to proceed with dimerization reaction at 10°C. for 5 hours under stirring. The resultant reaction mixture, afterwashed with a dilute aqueous solution of sodium hydroxide and saturatedbrine, was hydrogenated in an autoclave having a capacity of one literin the presence of 15 g of a hydrogenation nickel/diatomaceous earthcatalyst added therein (available from Nikki Chemical Industrial Co.,Ltd. under the trade name N-113) under a hydrogen pressure of 3 MPa·G ata reaction temperature of 250° C. for 5 hours. After the completion ofthe reaction, the catalyst was removed by filtration and the filtratewas subjected to vacuum distillation to obtain 340 g of an objectivedimer as hydrogenated product (hereinafter referred to as Fluid A). Theproperties of the Fluid A, the results of ultrasonic shear stabilitytest (JPI-5S-29-88) and the results of traction coefficient measurementare given in Table 1.

Reference Example 2

In a four-neck flask equipped with a reflux condenser, a stirrer and athermometer and having a capacity of 500 milliliter, were placed 4 g ofactivated clay (available from Mizusawa Chemical Industrial Co., Ltd.under the trade name Galeon Earth), 10 g of diethylene glycol monoethylether and 200 g of α-methylstyrene, and the content therein was heatedto a reaction temperature of 105° C. under stirring for 4 hours. Afterthe completion of the reaction, the resultant reaction mixture wasanalyzed by gas chromatography, and thus was proved to be the objectivelinear dimer of α-methylstyrene at 70% conversion and 95% selectivity, acyclic dimer of α-methylstyrene as a byproduct at 1% selectivity and atrimer of high boilng point at 4% selectivity. By subjecting thereaction mixture to hydrogenation and vacuum distillation in the samemanner as in Reference Example 1, there was obtained 125 g ofhydrogenated linear dimer of α-methylstyrene having purity of 99%, thatis, 2,4-dicyclohexyl-2-methylpentane (hereinafter referred to as FluidB). The properties of the Fluid B, the results of ultrasonic shearstability test (JPI-5S-29-88) and the results of traction coefficientmeasurement are given in Table 1.

Example 1

An autoclave having a capacity of one liter were placed 15 g of ahydrogenation nickel/diatomaceous earth catalyst (available from NikkiChemical Industrial Co., Ltd. under the trade name N-113), 20 g ofpolystyrene (M_(W): 160,000) and 500 milliliter of cyclohexane to carryout hydrogenation reaction under a hydrogen pressure of 6 MPa·G at areaction temperature of 250° C. for 3 hours. After cooling the reactionproduct, the catalyst was removed by filtration and the filtrate wassubjected to evaporation to bone dryness, followed by vacuumdistillation to obtain 19 g of hydrogenated polystyrene (hereinafterreferred to as Polymer “a”). As the result of the measurement thereof bymeans of GPC, the Polymer “a” had a weight average molecular weight of14,000 expressed in terms of polystyrene. The Polymer “a” at a ratio of1.5% by mass was mixed with the Fluid A of Reference Example 1 to obtaina fluid composition. The properties of the fluid composition, theresults of ultrasonic shear stability test (JPI-5S-29-88) and theresults of traction coefficient measurement are given in Table 1.

Example 2

The procedure in Example 1 was repeated except that the hydrogenationreaction was performed for 30 minutes by the use of 20 g ofethylene/styrene copolymer (styrene 63 mole %, M_(W): 160,000) in placeof 20 g of polystyrene (M_(W): 160,000). Thus there was obtained 19 g ofhydrogenated product of ethylene/styrene copolymer (hereinafter referredto as Polymer “b”). As the result of the measurement thereof by means ofGPC, the Polymer “b” had a weight average molecular weight of 18,000expressed in terms of polystyrene. The Polymer “b” at a ratio of 1.5% bymass was mixed with the Fluid A of Reference Example 1 to obtain a fluidcomposition. The properties of the fluid composition, the results ofultrasonic shear stability test (JPI-5S-29-88) and the results oftraction coefficient measurement are given in Table 1.

Example 3

The procedure in Example 1 was repeated except that the hydrogenationreaction was performed for 40 minutes by the use of 20 g ofethylene/styrene copolymer (styrene 50 mole %, M_(W): 200,000) in placeof 20 g of polystyrene (M_(W): 160,000). Thus there was obtained 19 g ofhydrogenated product of ethylene/styrene copolymer (hereinafter referredto as Polymer “c”). As the result of the measurement thereof by means ofGPC, the Polymer “c” had a weight average molecular weight of 9,000expressed in terms of polystyrene. The Polymer “c” at a ratio of 1.5% bymass was mixed with the Fluid A of Reference Example 1 to obtain a fluidcomposition. The properties of the fluid composition, the results ofultrasonic shear stability test (JPI-5S-29-88) and the results oftraction coefficient measurement are given in Table 1.

Comparative Example 1

The procedure in Example 3 was repeated except that the hydrogenationreaction was performed at the temperature of 200° C. for 4 hours inplace of at the temperature of 250° C. for 40 minutes. Thus there wasobtained 19 g of hydrogenated product of ethylene/styrene copolymer(hereinafter referred to as Polymer “d”). As the result of themeasurement thereof by means of GPC, the Polymer “d” had a weightaverage molecular weight of 120,000 expressed in terms of polystyrene.The polymer “d” at a ratio of 1.5% by mass was mixed with the Fluid A ofReference Example 1 to obtain a fluid composition. The properties of thefluid composition, the results of ultrasonic shear stability test(JPI-5S-29-88) and the results of traction coefficient measurement aregiven in Table 1.

Comparative Example 2

The procedure in Example 3 was repeated except that the hydrogenationreaction was performed at the temperature of 250° C. for 4 hours inplace of 250° C. for 40 minutes. Thus there was obtained 19 g ofhydrogenated product of ethylene/styrene copolymer (hereinafter referredto as Polymer “e”). As the result of the measurement thereof by means ofGPC, the Polymer “e” had a weight average molecular weight of 5,000expressed in terms of polystyrene. The Polymer “e” at a ratio of 1.5% bymass was mixed with the Fluid A of Reference Example 1 to obtain a fluidcomposition. The properties of the fluid composition, the results ofultrasonic shear stability test (JPI-5S-29-88) and the results oftraction coefficient measurement are given in Table 1.

Comparative Example 3

Ethylene/propylene copolymer available on the market (available fromMitsui Chemical Industrial Co., ltd. under the trade name “LucantHC-3000X”, weight average molecular weight of 18,000 expressed in termsof polystyrene) at a ratio of 1.5% by mass was mixed with the Fluid A ofReference Example 1 to obtain a fluid composition. The properties of thefluid composition, the results of ultrasonic shear stability test(JPI-5S-29-88) and the results of traction coefficient measurement aregiven in Table 1.

Example 4

Polymer “b” obtained in Example 2 at a ratio of 1.5% by mass was mixedwith the Fluid B of Reference Example 2 to obtain a fluid composition.The properties of the fluid composition, the results of ultrasonic shearstability test (JPI-5S-29-88) and the results of traction coefficientmeasurement are given in Table 1.

Example 5

In a one liter autoclave were placed 15 g of a hydrogenationnickel/diatomaceous earth catalyst (available from Nikki ChemicalIndustrial Co., Ltd. under the trade name N-113), 20 g ofpolyisobutylene (available from BASF corporation under the trade name“OPPANOL·B10, weight average molecular weight of 47,000 expressed interms of polystyrene) and 500 milliliter of cyclohexane to carry outhydrogenation reaction under a hydrogen pressure of 5 MPa·G at areaction temperature of 280° C. for 8 hours. After cooling the reactionproduct, the catalyst was removed by filtration and the filtrate wassubjected to evaporation to bone dryness followed by vacuum distillationto obtain 19 g of hydrogenated polyisobutylene (hereinafter referred toas Polymer “f”). As the result of the measurement thereof by means ofGPC, the Polymer “f” had a weight average molecular weight of 32,000expressed in terms of polystyrene. The Polymer “f” at a ratio of 1.5% bymass was mixed with the Fluid B of Reference Example 2 to obtain a fluidcomposition. The properties of the fluid composition, the results ofultrasonic shear stability test (JPI-5S-29-88) and the results oftraction coefficient measurement are given in Table 1.

Comparative Example 4

Polyisobutylene (available from BASF corporation under the trade name“OPPANOL·B10, weight average molecular weight of 47,000 expressed interms of polystyrene) at a ratio of 1.5% by mass was mixed with theFluid B of Reference Example 2 to obtain a fluid composition. Theproperties of the fluid composition, the results of ultrasonic shearstability test (JPI-5S-29-88) and the results of traction coefficientmeasurement are given in Table 1.

Example 6

Ethylene/α-methylstyrene copolymer which had been produced throughpolymerization (α-methylstyrene moiety of 50 mole %, weight averagemolecular weight of 13,000 expressed in terms of polystyrene) at a ratioof 1.5% by mass was mixed with the Fluid B of Reference Example 2 toobtain a fluid composition. The properties of the fluid composition, theresults of ultrasonic shear stability test (JPI-5S-29-88) and theresults of traction coefficient measurement are given in Table 1.

Example 7

Ethylene/norbornene copolymer which had been produced throughpolymerization (norbornene moiety of 40 mole %, weight average molecularweight of 23,000 expressed in terms of polystyrene) at a ratio of 1.5%by mass was mixed with the Fluid B of Reference Example 2 to obtain afluid composition. The properties of the fluid composition, the resultsof ultrasonic shear stability test (JPI-5S-29-88) and the results oftraction coefficient measurement are given in Table 1.

Example 8

Ethylene/dicyclopentadiene copolymer which had been produced throughpolymerization (dicyclopentadiene moiety of 50 mole %, weight averagemolecular weight of 38,000 expressed in terms of polystyrene) at a ratioof 1.5% by mass was mixed with the Fluid B of Reference Example 2 toobtain a fluid composition. The properties of the fluid composition, theresults of ultrasonic shear stability test (JPI-5S-29-88) and theresults of traction coefficient measurement are given in Table 1.

Measurements were made of the traction coefficients in examples andcomparative examples by the use of a two-cylinder friction tester.Specifically, traction coefficients were determined by means of twocylinders in contact with each other in cylindrical direction which hadsame diameter of 52 mm and a thickness of 6 mm and which were composedof a drum-shaped driven cylinder with a curvature radius of 10 mm and aflat driving cylinder without crowning by rotating either one at aconstant velocity and other one at a continuously varied velocity,applying a load of 98.0 N to the contact portion of both the cylindersby means of a weight, and measuring the tangent force generating betweenboth the cylinders, that is, the objective traction coefficient.Therein, the cylinders were made of bearing steel SUJ and mirrorfinished, the average peripheral velocity was 6.8 m/second, and maximumhertz contact pressure was 1.23 GPa. In measuring the tractioncoefficient of the fluid at a fluid temperature (oil temperature) of140° C., the oil temperature was raised to 140° C. from 40° C. byheating an oil tank with a heater, whereby the traction coefficientthereof was determined at a slip factor of 5%. TABLE 1 ReferenceReference Comp. Comp. Example 1 Example 2 Example 1 Example 2 Example 3Example 1 Example 2 Kinematic 17.32 20.23 22.01 24.05 21.27 42.72 20.68viscocity @ 40° C., mm²/s Kinematic 3.578 3.572 4.307 4.649 4.162 7.9714.033 viscosity @ 100° C., mm²/s Viscosity index 77 13 101 110 94 161 85Viscosity decrease −0.1 −0.1 −0.6 −0.9 −0.5 −31.5 −0.2 after shearstability test, % Traction 0.077 0.070 0.077 0.077 0.077 0.077 0.077coefficient @ 140° C. Comp. Comp. Example 3 Example 4 Example 5 Example4 Example 6 Example 7 Example 8 Kinematic 23.18 26.41 28.31 32.48 24.8725.06 26.12 viscocity @ 40° C., mm²/s Kinematic 4.622 4.53 4.84 5.3394.275 4.737 4.891 viscosity @ 100° C., mm²/s Viscosity index 116 72 8795 56 108 110 Viscosity decrease −0.7 −0.9 −0.9 −7.3 −2.8 −1.1 −2.3after shear stability test, % Traction 0.074 0.071 0.07 0.07 0.07 0.0770.077 coefficient @ 140° C.

TABLE 1-2 Comp. Comp. Comp. Example 2 Example 3 Example 4 Example 5Example 4 Example 6 Example 7 Example 8 Kinematic 20.68 23.18 26.4128.31 32.48 24.87 25.06 26.12 viscosity @ 40° C., mm²/s Kinematic 4.0334.622 4.53 4.84 5.339 4.275 4.737 4.891 viscosity @ 100° C., mm²/sViscosity 85 116 72 87 95 56 108 110 index Viscosity −0.2 −0.7 −0.9 −0.9−7.3 3‘2.8 −1.1 −2.3 decrease after shear stability test, % Traction0.077 0.074 0.071 0.07 0.07 0.077 0.077 coefficient @ 140° C.

It is understandable from Table 1 that in comparison with thecomparative examples, the examples have brought about improved viscosityindex and excellent shear stability without lowering tractioncoefficient.

In addition thereto, the present invention not only has brought aboutenhanced viscosity index merely due to enhanced kinematic viscosity, butalso has optimized the following three respects:

(1) Even the viscosity is increased, the performance of enhancingviscosity index is different depending upon the polymer to be added.

(2) Conventional polymer as a viscosity index improver, even when addedin a small amount, greatly lowers the traction coefficient.

(3) The performance of enhancing viscosity index increases, but theshear stability decreases with an increase in the molecular weight ofthe polymer,

INDUSTRIAL APPLICABILITY

The traction drive fluid composition according to the present inventionis improved in viscosity index and is excellent in shear stabilitywithout being lowered in traction coefficient, can be practicallyutilized as a traction drive system CVT oil all over the world.

1. A traction drive fluid composition which comprises component (A) abase oil for traction drives bearing at least one selected from aquaternary carbon atom or an alicyclic structure in the molecule andcomponent (B) at least one polymer having a weight average molecularweight in the range of 8,000 to 40,000 and which is selected from among(a) hydrocarbon polymers each comprising as a constituent at least 10mole % of a monomer bearing a cyclic structure, (b) hydrocarbon polymerseach comprising at least 25% of quaternary carbon atoms in the backbonechain, and (c) hydrogenated products from the polymers (a) and (b). 2.The traction drive fluid composition according to claim 1, wherein thepolymer as the component (B) has a weight average molecular weight inthe range of 9,000 to 38,000.
 3. The traction drive fluid compositionaccording to claim 1, wherein the base oil as the component (A) has atraction coefficient at 140° C. of at least 0.070, kinematic viscosityat 40° C. in the range of 10 to 25 mm²/s, a viscosity index of at least60, a pour point of minus 40° C. or lower and a flash point of 100° C.or higher.
 4. The traction drive fluid composition according to claim 1,wherein the polymer as the component (B) is blended in an amount of 0.1to 20% by mass based on the composition with the base oil as thecomponent (A).
 5. The traction drive fluid composition according toclaim 1, wherein the polymer as the component (B) is blended in anamount of 0.5 to 5% by mass based on the composition with the base oilas the component (A).
 6. The traction drive fluid composition accordingto claim 2, wherein the base oil as the component (A) has a tractioncoefficient at 140° C. of at least 0.070, kinematic viscosity at 40° C.in the range of 10 to 25 mm²/s, a viscosity index of at least 60, a pourpoint of minus 40° C. or lower and a flash point of 100° C. or higher.